This invention relates generally to strut type suspension members which utilize airsprings in conjunction with a damping member contained therein. In particular, conventional hydraulic shock absorbers provide the damping means and rolling lobe type airsprings provide the load support. The geometry used on helical spring strut suspensions for automobiles is such that the vehicle mass produces an angular displacement or torque which causes bending of the strut. This bending moment to the strut causes binding of the shock absorber piston which results in ride harshness. This harshness is pronounced at low amplitude undulation of the vehicle. Conventional helical coil spring MacPherson struts utilize a coil spring that is both offset and set at an angle to the strut axis. This geometry is an attempt to create compensating side loading to oppose the stress placed on the strut by the spring mass of the vehicle.
The helical spring type struts, as represented by a MacPherson strut configuration cannot be adjusted to compensate for increased vehicle load. Thus, as load increases vehicle height decreases. Also, the coil spring is limited to a single or at best a very narrow range of spring rates which requires a design selection between a soft ride and a hard ride.
An object of this invention is to provide a suspension strut utilizing an airspring which generates side load compensating force. This force counteracts the bending torque created by the mass of the vehicle in operation and minimizes stiction in the hydraulic damper of the strut. This yields a softer ride, variable spring rates, also, a constant vehicle height can be maintained regardless of load by adjusting the internal pressure in the airspring portion of the strut.
One embodiment of the invention utilizes a nonsymmetrical or eccentric airspring piston configuration in which the rolling lobe or meniscus of the airspring flexible member on opposing sides of the airspring piston are of unequal axial length. This nonsymmetric configuration creates compensating side load and allows the airspring to be mounted without an offsetting angle to the shock absorber piston rod. This non-offset mounting makes for a space efficient strut configuration. A further advantage of this configuration is that the airspring piston diameter can be maintained at a minimum to provide a low spring rate and softer vehicle ride.
In another embodiment, the airspring acts at an angle to the axis of rotation of strut to create side loading force. Yet another embodiment utilizes a flexible member of the airspring which is of unequal axial length around the circumference of the flexible member which creates side loading when attached to the airspring piston and upper retainer.